The present invention relates to an electrochemical meter for measuring the concentration of carbon within a fluid and, more particularly, to such a device which is quite reliable and accurate and is especially designed to measure the concentration of carbon in molten sodium.
It is desirable for various purposes to be able to measure the concentration or activity of carbon in a fluid, such as in a liquid metal or high temperature gas used in an industrial process or commercial equipment. For example, it is quite important to be able to monitor the activity of carbon in the molten sodium heat transfer loops of liquid metal, fast breeder fission reactors. The carbon activity in the sodium is a measure of the detrimental carbonization and decarbonization of the piping, heat exchangers, etc., in contact with the molten sodium.
Various types of carbon activity meters have been designed to measure the activity of carbon in molten sodium. Reference is made to Report No. ANL-8017 available from N.T.I.S., U.S. Department of Commerce, 5285 Port Royal Road, Springfield VA. 22151, for examples of meters designed for this purpose. As will be seen, many of such meters are of the so-called diffusion type. Such meters rely on the diffusion of free carbon from the sodium into a gas stream for later analysis to determine the amount of carbon picked up thereby. One of the primary difficulties with such meters is that a relatively cumbersome gas phase analysis procedure is required for their use. Moreover, such diffusion meters are only capable of indicating changes in the carbon activity, rather than provide absolute measurements of the amount of carbon activity. Other meters have been designed which are, in effect, electrochemical cells. Most electrochemical carbon meters, as they are called, use molten alkali metal carbonate as an electrolyte. Such designs are typically unacceptable because of the corrosive nature of the carbonate electrolyte and their inability to detect carbon activity at the levels which are generally found in liquid sodium-stainless steel systems.
In order to circumvent some of the above problems, an electrochemical carbon meter has been designed which uses a carbon activity gas as an intermediary between the molten sodium and an electrochemical cell. Such meter is fully described in the W. Ruther et al paper appearing in Nuclear Technology, Volume 21, page 75, (1974). While this meter circumvents some of the problems of meters of earlier designs, it has its own difficulties. A major one is that the intermediary gas activity is affected by variables other than the amount of carbon which is diffused into it from the sodium. While attempts have been made to correct the inaccuracies inherent in it in view of such uncontrolled variables by, for example, periodically adjusting the total pressure of the gas, the necessity of such corrective factors has made use of the meter for continuous on-line carbon activity monitoring unwieldy.